SIST EN ISO 11819-1:2002

SLOVENSKI STANDARD
01-september-2002
Acoustics - Measurement of the influence of road surfaces on traffic noise - Part 1:
Statistical Pass-By method (ISO 11819-1:1997)
Acoustics - Measurement of the influence of road surfaces on traffic noise - Part 1:
Statistical Pass-By method (ISO 11819-1:1997)
Akustik - Messung des Einflusses von Straßenoberflächen auf Verkehrsgeräusche - Teil
1: Statistisches Vorbeifahrtverfahren (ISO 11819-1:1997)
Acoustique - Mesurage de l'influence des revetements chaussées sur le bruit émis par la
circulation - Partie 1: Méthode statistique au passage (ISO 11819-1:1997)
Ta slovenski standard je istoveten z: EN ISO 11819-1:2001
ICS:
17.140.30 Emisija hrupa transportnih Noise emitted by means of
sredstev transport
93.080.20 Materiali za gradnjo cest Road construction materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 11819-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2001
ICS 17.140.30
English version
Acoustics - Measurement of the influence of road surfaces on
traffic noise - Part 1: Statistical Pass-By method (ISO 11819-
1:1997)
Acoustique - Mesurage de l'influence des revêtements Akustik - Messung des Einflusses von Straßenoberflächen
chaussées sur le bruit émis par la circulation - Partie 1: auf Verkehrsgeräusche - Teil 1: Statistisches
Méthode statistique au passage (ISO 11819-1:1997) Vorbeifahrtverfahrtverfahren (ISO 11819-1:1997)
This European Standard was approved by CEN on 11 June 2001.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2001 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11819-1:2001 E
worldwide for CEN national Members.

Foreword
The text of the International Standard from Technical Committee ISO/TC 43 "Acoustics" of the
International Organization for Standardization (ISO) has been taken over as an European
Standard by Technical Committee CEN/TC 227 "Road materials", the secretariat of which is held
by DIN.
This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by February 2002, and conflicting national
standards shall be withdrawn at the latest by February 2002.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium, Czech
Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg,
Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom.
NOTE FROM CMC The foreword is susceptible to be amended on reception of the German language
version. The confirmed or amended foreword, and when appropriate, the normative annex ZA for the
references to international publications with their relevant European publications will be circulated with the
German version.
Endorsement notice
The text of the International Standard ISO 11819-1:1997 has been approved by CEN as a
European Standard without any modification.
INTERNATIONAL
IS0
STANDARD
11819-I
First edition
1997-09-l 5
Acoustics -
Measurement of the influence
of road surfaces on traffic noise -
Part 1:
Statistical Pass-By method
Acoustique - Mesurage de /‘influence des rev&tements de chaus&es sur
le bruit 4mis par la circulation -
Partie 1: Mgthode statistique au passage
Reference number
IS0 118194:1997(E)
IS0 11819=1:1997(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for which
a technical committee has been established has the right to be represented
on that committee. International organizations, governmental and non-
governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 118194 was prepared by Technical Committee
ISOmC 43, Acoustics, Subcommittee SC 1, Noise.
IS0 11819 consists of the following parts, under the general title
Acoustics - Measurement of the influence of road surfaces on traffic
noise:
- Part I: Statistical Pass-By method
- Part 2: Close-proximity method
Annexes A to F of this part of IS0 11819 are for information only.
0 IS0 1997
All rights reserved. Unless otherwise specified, no part of this publication may be
reproduced or utilized in any form or by any means, electronic or mechanical, including
photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Internet central @ iso.ch
x.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
ii
ISO11819-1:1997( E)
Introduction
The emission and propagation of road traffic noise greatly depend on road surface characteristics,
notably on texture and porosity. Both these characteristics influence the generation of tyre/road noise
and, in addition, the porosity can influence the propagation of sound, particularly when the propagation
takes place close to the surface. Power unit noise, which is usually generated at a greater height
above the road surface than tyre/road noise, may also be affected during propagation by the porosity
characteristics of the road surface. These effects lead to differences in sound levels, associated with a
given traffic flow and composition, from different road surfaces of up to 15 dB, which can have a
substantial impact on the environmental quality alongside a road.
It is therefore important to be able to measure this influence by a standardized method and to arrive at
a quantitative ranking of road surfaces with respect to traffic noise. This part of IS0 11819 offers such
a method, the objective of which is to satisfy a need expressed by road planners, road administrators,
contractors, manufacturers of so-called “low-noise surfaces” and by other parties concerned with the
prediction and control of road traffic noise.

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INTERNATIONAL STANDARD @ Iso IS0 118194 : 1997(E)
- Measurement of the influence of road surfaces on
Acoustics
traffic noise -
Part 1:
Statistical Pass-By method
Scope
This part of IS0 11819 describes a method of comparing traffic noise on different road surfaces for
various compositions of road traffic for the purpose of evaluating different road surface: types. Sound
levels representing either light or heavy vehicles at selected speeds are assigned to a certain road
surface. The method is applicable to traffic travelling at constant speed, i.e. free-flowingconditions at
posted speeds of 50 km/h and upwards. For other driving conditions where traffic is not free-flowing,
such as at junctions and where the traffic is congested, the road surface is of less importance.
A standard method for comparing noise characteristics of road surfaces gives road and,,environment
authorities a tool for establishing common practices or limits as to the use of surfacings meeting
certain noise criteria. However, it is not within the scope of IS0 11819 to suggest such criteria.
The Statistical Pass-By (SPB) method is intended to be used essentially for two main purposes. First it
may be used to classify surfaces in typical and good condition as a type according to their influence on
traffic noise (surface classification) and, secondly, it may be used to evaluate the influence on traffic
noise of different surfaces at particular sites irrespective of condition and age. This ,tatter type of
application may be useful for example where a road is to be resurfaced and “before” and “after”
measurements are required in order to assess the differences in traffic noise followingresurfacing.
generally be used for approval of works at any given site.
Clause 4 gives a general description of the SPB method.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions
of this part of IS0 11819. At the time of publication, the editions indicated were valid. All standards are
subject to revision, and parties to agreements based on this part of IS0 11819 are encouraged to
investigate the possibility of applying the most recent editions of the standards indicated below.
Members of IEC and IS0 maintain registers of currently valid International Standards.
IS0 10844:1994, Acoustics - Test surface for road vehicle noise measurement.
Characterization of pavement texture using surface profiles - Part
IS0 13473-l :1997, Acoustics -
1: Determination of mean profile depth.
IEC 60651: 1979, Sound /eve/ meters.
I EC 60942: 1988, Sound calibrators.
I EC 61260: 1995, Hectroacoustics - Octave-band and fractional-octave-band filters.
IS0 118194 :1997(E)
3 Definitions
For the purposes of this part of IS0 11819, the following definitions apply.
Traffic noise, vehicle noise, tyrekoad noise and power unit noise
3.1
3.1 .l traffic noise
overall noise emitted by the traffic running on the road under study
3.1.2 vehicle noise
total noise from an individual vehicle, the two major components of which are power unit noise (3.1.4)
and tyre/road noise (3.1.3)
3.1.3 tyre/road noise
noise generated by the tyre/road interaction
3.1.4 power unit noise
noise generated by the vehicle engine, exhaust system, air intake, fans, transmission, etc.
Statistical Pass-By (SPB) method
3.2
measurement procedure designed to evaluate vehicle and traffic noise generated on different sections
of road surface under specific traffic conditions
NOTE - The measurements are taken from a great number of vehicles operating normally on the road. Results
obtained using this procedure are normalized to standard speeds according to the category or type of road
being considered.
3.3 Road speed categories
Three categories of roads are defined with respect to the range of speeds at which the traffic flows
and these are usually associated with certain areas (urban, suburban, rural, etc.).
3.3.1 “low” road speed category
conditions which relate to traffic operating at an average speed of 45 km/h to 64 km/h
NOTE - These conditions are usually associated with urban traffic.
3.3.2 “medium” road speed category
conditions which relate to traffic operating at an average speed of 65 km/h to 99 km/h
NOTE - These conditions are mostly found in suburban areas or on rural highways.
3.3.3 “‘high” road speed category
conditions which relate to cars operating at an average speed of 100 km/h or more; heavy vehicles
may operate at lower average speed due to speed restrictions
NOTE - These conditions are usually associated with motorway traffic in rural or suburban areas.
IS0 11819-l : 1997(E)
3.4 Vehicle categories
A vehicle category consists of vehicles which have certain common features easy to identify in the
traffic stream, such as the number of axles and the size. The common (features are assumed to
correspond to similarities in their sound emission when driven under the same operating conditions.
The following vehicle categories are considered to be sufficient for Tdescription of the noise
characteristics of road surfaces and are used in this part of IS0 11819 (see-also annex A).
3.4.1 Category No. 1 - cars
passenger cars excluding other light vehicles
3.4.2 Category No. 2 - heavy vehicles
all trucks, buses and coaches with at least two axles and more than four wheels
NOTE - This category consists of Categories 2a and 2b together.
3.4.2.1 Category No. 2a - dual-axle heavy vehicles
trucks, buses and coaches with two axles and more than four wheels
3.4.2.2 Category No. 2b - multi-axle heavy vehicles
trucks, buses and coaches with more than two axles
35 . maximum sound level
highest sound pressure level recorded by the measuring instrument during1.a vehicle pass-by, using
the appropriate frequency weighting and time weighting F, for vehicles which are acoustically
identifiable, i.e. are not significantly disturbed by other vehicles (see also 7.2)
Vehicle Sound Level, Lveh
3.6
maximum A-weighted sound pressure level determined at a reference speed:from a regression line of
the maximum A-weighted sound pressure level versus the logarithm of speed, calculated for each
vehicle category
Statistical Pass-By Index (SPBI)
3.7
noise index for comparison of road surfaces, that is based on the Vehicle Sound Levels and takes into
account the mix and speeds of vehicles
38 . reference surface
surface selected according to the purpose of the measurement, following certain rules listed in this
part of IS0 11819; levels on the reference surface are normalized to zero level-,(0 dB) and levels on all
other surfaces are presented as differences from this reference level
NOTE - The main purpose of this method is to compare road surfaces with respect1 to traffic noise emission.
Sound levels measured on a certain surface may, therefore, be presented in comparison to sound levels
measured on another surface which is then considered as a reference surface.
39 . absorptive surfaces
1) For road or ground surfaces: surface for which a substantial part of the incident acoustical energy is
absorbed
EXAMPLES - Typical absorptive surfaces are loose gravel, sand, some porous pavements and
ground covered by grass, ivy, or other low-growing vegetation.
IS0 11819-I : 1997(E)
2) For noise barriers: type of surface with which some noise barriers are equipped on the source side
with the intention of reducing sound reflections
4 Measuring principle
In the Statistical Pass-By (SPB) method, the maximum A-weighted sound pressure levels of a
statistically significant number of individual vehicle pass-bys are measured at a specified road-side
location together with the vehicle speeds. Each measured vehicle is classified into one of three vehicle
categories: “cars”, “dual-axle heavy vehicles” and “multi-axle heavy vehicles”. Other vehicle categories
are not used for this evaluation, since they do not provide any additional information regarding road
surface influence.
For each of three speed ranges defined in 3.3, as well as for each of the three vehicle categories, a
nominated reference speed is given. Each individual pass-by level together with its vehicle speed is
recorded, and a regression line of the maximum A-weighted sound pressure level versus the
logarithm of speed is calculated for each vehicle category. From this line, the average maximum A-
weighted sound pressure level is determined at the reference speed. This level is called the Vehicle
Sound Level, Lveh.
For the purpose of reporting the acoustic performance of road surfaces the Vehicle Sound Levels for
cars, dual-axle heavy vehicles and multi-axle heavy vehicles are added on a power basis, assuming
certain proportions of these vehicle categories, to give a single “index” which constitutes the final
result. This index is called the Statistical Pass-By Index (SPBI) and can be used for comparison of
road surfaces so that their influence on sound level of a mixed traffic flow can be determined. It is not
suitable for determining actual traffic noise levels.
5 Measuring instruments
. Sound level instrumentation
The sound level meter (or the equivalent measuring system) shall meet the requirements of a Type 1
instrument according to IEC 60651.
A windscreen shall be used and should be of a type specified by the microphone manufacturer as
suitable for the particular microphone. It should be ascertained from the manufacturer that the
windscreen does not detectably influence the performance of the sound level meter under the ambient
conditions of the test.
Frequency analysis instrumentation
5.2
Frequency analysis of the measured sound using one-third-octave band resolution is recommended,
but not mandatory. The frequency range of 50 Hz to 10 000 Hz (centre frequencies of one-third-octave
bands) shall be covered. The one-third-octave-band filters shall conform to IEC 61260.
5.3 Calibration
At the beginning of the measurements, and following any warm-up time specified by the manufacturer,
the overall sensitivity of the sound level meter or the equivalent measuring system (including the
microphone) shall be checked. If necessary, it shall be adjusted according to the manufacturer’s
instructions. This may require use of a sound calibrator. These checks shall be repeated at the end
of the measurements and the values obtained recorded. Any deviations shall be recorded in the test
report. If the calibration readings on the sound level meter differ by more than 0,5 dB during a series
of measurements, the test shall be considered invalid. The same procedure shall be followed if a
frequency analyser is used.
IS0 11819-I :I 997(E)
The sound calibrator device shall meet the requirements of IEC 60942, Class0 or Class 1.
The compliance of the sound calibrator with the requirements of the appropriate class of IEC 60942
shall be verified annually. The compliance of the sound level meter, or equivalent measuring system,
with the requirements of IEC 60651 shall be verified at least every two yearsLThis shall be performed
by a laboratory accredited or otherwise authorized to perform calibrations traceable to the national
standards.
5.4 Vehicle speed measurement instrumentation
The vehicle speed at the instant when the vehicle passes the microphoneshall be measured with a
standard uncertainty of less than =t 3%. Measuring devices which rest on the road surface and are
activated by the passage of vehicle tyres should not be used.
5.5 Temperature measurement instrumentation
The temperature measuring instrument(s) shall have a maximum permiss,ibte error of 1 OC. Meters
using an infrared technique shall not be used for air temperature measurements.
6 Test sites
61 . Selection of measuring site
The following considerations apply for site selection.
Each road test section shall extend at least 30 m on both sides from the: microphone location. For
a)
the “high” road speed category this distance is increased to 50 m.
b) The road shall be essentially level and straight. Roads with slight bends or with gradient < 1 %
may be considered as valid test sites for the purposes of this part of ISO:lJl 819.
c) The number of vehicles judged to be moving at constant speed shall ibe sufficient in order to
allow a reasonable total measuring time.
The requirements on background noise at the test site according to clause 12 shall be observed.
See also 7.2 regarding selection of vehicles.
e) The road surface should be in a good condition, unless the intention ,is to study the effect of
condition, and be homogeneous over the entire test section. Road surfaces which exhibit
unusually high unevenness characteristics, surface cracking, bitumen bleeding, excessive stone
loss or contain expansion joints, for example, would not normally be considered as suitable for
surface classification purposes.
The traffic flowing on the road section of interest should contain sufficient numbers of each
f )
category of vehicle to enable a full analysis of each vehicle category to be carried out.
road surfaces change their noise characteristics rather quickly after opening for
NOTE - Since some types of
laid surfaces have limited validity.
traffic, measurements on newly
6.2 Paired and single site measurements
Measurements described in this part of IS0 11819 will commonly be taken at a single test surface and
then compared with similar measurements taken at other surfaces where traffic may be different.
However, in some cases, the noise characteristics of different surfaces can be compared by taking
IS0 11819-I : 1997(E)
@ IS0
simultaneous measurements on two or more road sections where the surfaces to be compared have
been laid in adjacent road sections. These are referred to as ‘paired’ measurements since the
measurement technique employs the selection of the same vehicles from the traffic stream as they
pass each measurement site.
The use of this technique will improve the accuracy of the comparison due to the elimination of
differences in traffic composition and climate.
From 6.1 it follows that the measurement locations will need to be separated along the road by at least
60 m (100 m for the “high” road speed category).
paired sites, for exa .mple due to se lection specified in 7.2, shall also
Vehicles excluded from one of the
site.
be excluded from the other paired
6.3 Deviations from free-field conditions
For surface classification purposes, the measurement microphone should be located in the acoustical
free field. In practice, this means that acoustic reflections from surfaces such as building facades,
noise barriers, road cuttings and embankments shall be at least 10 dB lower than the direct sound to
be measured. As a guideline, 25 m of space around the microphone free of any reflecting objects
other than the ground is usually adequate to ensure that approximate free field conditions exist.
6.4 Considerations of guard rails and other barriers which may reflect or screen the sound
There shall be no large reflecfing surfaces, such as solid safety barriers or embankments, within
10 m of a line drawn from the measuring microphone position, crossing the roadway perpendicular to
the line of travel. This is precisely shown as a rectangle in figure la). If safety barriers are present
within the rectangle, they shall be covered with effective sound absorbing material prior to the
measurements. The presence of such surfaces and the type of covering shall be duly stated in the
report.
It is necessary to temporarily remove a short section of any safety barrier or guard rail located in front
of the measurement microphone to ensure that minimal screening from the obstacles occurs at the
measurement location. Within the part of the rectangle shown in figure la) which is between the road
and a line parallel to the road and which goes through the microphone position, there shall be no
potentially screening roadside barrier or guard rail.
Protective fences will not normally affect the results and can be ignored for the purpose of site and
microphone position selection. Treatments on some noise barriers with the intention to reduce sound
reflections are not sufficiently absorptive to allow such barriers within the rectangle shown in figure
.
Ia)
NOTE 1 In IS0 11819, a solid safety barrier is a concrete wall structure designed to prevent vehicles from
leaving the road or crossing the median.
NOTE 2 In IS0 11819, a guard rail is a structure consisting of a metal beam or plate attached to rigid posts and
designed to prevent vehicles from leaving the road or crossing the median. There is also a type of guard rail
consisting of stretched steel wires attached to rigid posts.
NOTE 3 In IS0 11819, a protective fence is a structure fabricated of wire or cable (usually chain link) mounted
on support posts and intended to prevent animals or human beings of entering the road.

IS0 11819-l :1997(E)
median marking
--.-.l.“-L.l----l-lIL
centre of test lane
-------.~.~.~I-
No reflecting solid safety barrier allowed within this rectangle
unless covered with sound absorptive material. No screening
rail or safety barrier allowed within the part of this rectangle
which is between the microphone position and the test lane
(darker shaded part)
a)
road-side area
Area with arbitrary covering;
grass or plants shall not be tall;
depressions shall be covered.
Microphone position
Min. area covered with material
having sound absorption similar
No requirements
to that of tested surface.
in this area.
b)
- Requirements regarding freedom from reflecting or screening safety barriers or
Figure 1
guard rails (upper part, Fig. la) and regarding the minimum coverage with
acoustically appropriate surface between the test lane and the microphone (lower
part, Fig. 1 b)
(Figure not to scale)
IS0 11819-l :1997(E)
6.5 Surface between the tested road surface and microphone
Ideally, the surface between the microphone position and the edge of the test lane should be covered
with the same material as the road surface in the measuring lane. However, at some sites it may not
be possible to achieve this condition. When measurements are being made for surface classification
purposes, it is necessary to ensure that at least half of the area between the centre of the test lane
and the microphone shall have acoustical properties similar to the surface under test, and be
essentially level with the road surface. See figure lb). This may be accomplished by placing an
appropriate covering material over non-conforming surfaces. The selection of this material is left to the
judgement of the person responsible for the measurement. Figure 1 b) shows the angles over which
the covering should be applied. If this practice is undertaken, full details shall be summarized in the
report.
The 3,75 m nearest the microphone may be grass or another surface with significant absorption. Any
vegetation in this area shall be kept as short as possible.
Any roadside ditch or other significant depression shall be at least 5 m from the centre of the test lane.
When these propagation conditions cannot be met, the site is not suitable for acoustical classification
measurements (note, however, the possibility specified in 8.1 and figure 3 of using a microphone on
the other side of the road in cases where it is difficult to meet the requirements with the “normal”
microphone position).
6.6 Special site conditions
In cases where the intention is to investigate the effect of a modification or other change in the road
surface, it may be desirable to make a “before/after” study. In such studies it is not necessary to meet
all the site requirements, as long as it can be ascertained that there are no changes of importance for
sound emission, propagation or reflections from the “before” until the “after” situations. One shall then
observe that significant changes in vegetation from season to season might have an influence.
Such special studies shall be duly identified as being “special” in the measuring protocol and any site
conditions at variance with the specifications given in 6.1 to 6.5 shall be reported.
Traffic conditions
7.1 Vehicle classification
Only vehicles which clearly fall within any of the categories described in 3.4 shall be measured. Where
there is any doubt in classifying a vehicle, the measurement for that vehicle shall be discarded from
the study.
A more detailed vehicle classification is optional. See annex A for the categories that should be used
in such cases.
7.2 Selection of vehicles for measurement
Measurements shall only be taken on individual vehicle pass-bys which can be clearly distinguished
acoustically from other traffic on the road. The following criteria shall be used to judge if a vehicle
pass-by is distinguishable.
a) Just prior to and just after the passage of a vehicle intended for measurement, the A-weighted
sound pressure level shall be at least 6 dB below the measured maximum A-weighted sound pressure
level during the pass-by. See figure 2.
IS0 11819-l :1997(E)
is 70
T3
-
Q)
-
m
2 65
'13
-t
cn
.-
P
4 60
-2 I 1 0 1 3
Time (S)
Figure 2 - Illustration of required signal-to-noise ratio for individual vehicle pass-bys
(The solid thick line shows the total sound level from two disturbing vehicles and the tested vehicle.)
NOTE - This will ensure that at the time when the maximum sound level is generated, the collective sound from
other traffic will be at least IO dB below the registered maximum level and will therefore have negligible effect on
the measured level.
b) When selecting vehic& for measurement, care should also be taken to ensure that sound from
other vehicles overtaking the target vehicle or passing on the other carriageway do not influence the
measured result. In these cases it is possible that the maximum sound level from the target vehicle
and other traffic will occur approximately simultaneously so that the peaks obtained are then
indistinguishable. Such measurements shall be discarded.
c) Additionally, vehicles which clearly exhibit unusual or atypical noise characteristics such as might
occur due to a faulty exhaust system, vehicle body rattles or audible warning devices shall be
discarded from the measurement. Vehicles with auxiliary equipment which emits audible sound should
also be discarded.
d) The sound levels should be measured only from vehicles judged to be ,moving at constant speed.
Individual vehicles judged to deviate significantly in their lateral position from the median axis of the
test lane shall be discarded from the analysis.
See also the conditions mentioned in clause 12.
7.3 Minimum number of vehicles
Provided the purpose of the measurement is surface classification, the minimum
number of vehicles
specified below applies.
ISO11819-1:1997( E) @ IS0
To ensure that random errors do not become unacceptably large, the following minimum numbers of
vehicles shall be measured, within each vehicle category:
*
min. 100
Category 1 (Cars):
I
*
min. 30
Category 2a (Dual-axle heavy vehicles):
*
min. 30
Category 2b (Multi-axle heavy vehicles):
*
Categories 2a and 2b together (Heavy vehicles) : min. 80
See also 9.6 regarding expected uncertainties.
NOTE - This means that, for example, if there are 30 vehicles in Category 2a, 50 vehicles are needed in
Category 2b in order that Categories 2a and 2b together contain at least 80 vehicles. The minimum numbers are
due to requirements on precision balanced against the time needed to measure the desired number of vehicles
in the actual traffic.
7.4 Road speed categories
For the classification of road surfaces, it is necessary to distinguish between three road speed
categories, as defined in 3.3. Each of the three categories is associated with a defined reference
speed to be used for normalization of sound levels; see also 9.2. The acoustical behaviour of road
surfaces may be different for these road speed categories.
The sound levels Lveh and the SPBI calculated from them (see 9.5) shall always be reported for at
least one of the road speed categories.
Measuring procedure
81 . Microphone position
The horizontal distance from the microphone position to the centre of the lane in which the vehicles to
be measured travel shall be 7,5 m * 0,l m. The microphone location is shown as “Position I” in
figure 3.
An exception is if there is a two-lane road (one lane per direction) and the right-side shoulder is too
narrow to provide a surface having the appropriate acoustical reflectivity (see 6.5), in which case,
“Position 2” shall be used (microphone distance is still 7,5 m).
In the case of a 2x2 lane road (refer to the upper half of figure 3), if the shoulder is too narrow to
provide the appropriate acoustical reflectivity according to 6.5, one shall first consider if it is practical
and safe to divert the traffic into the “fast” lane. If this is not the case, one may select the microphone
position 2 instead.
The above assumes right-hand traffic. In cases of left-hand traffic, the positions shall be reversed.
The microphone shall be located I,2 m k 0,l m above the plane of the road lane. Unless otherwise
indicated by the manufacturer of the sound level meter, its reference axis for free field conditions (see
IEC 651) shall be horizontal and directed perpendicularly towards the path of the vehicles.
8.2 Sound level measurement
During each vehicle pass-by the maximum A-weighted sound pressure level shall be measured using
time weighting F.
IS0 118194 : 1997(E)
@ IS0
2 x 2 lane motorway (or corresponding):
(e.g. grass or gravel)
(median area)
(e.g. grass or gravel)
microphone position I
\L*
(“roadside area”)
1 x 2 lane highway or street:
(e.g. grass or gravel)
(e.g. grass or gravel)
& * microphone position I
(“roadside area”)
Figure 3 -Typical road configurations and microphone positions
Frequency spectrum measurement (recommended)
8.3
It is recommended to measure one-third-octave band frequency spectra. The averaging time should
correspond to “F”. The spectrum should be captured when the A-weighted sound pressure level
during a vehicle pass-by is at its maximum.
@ IS0
IS0 118194 : 1997(E)
84 . Speed measurement
The vehicle speed at the moment when the vehicle midpoint passes the microphone shall be
measured. Paired measurements according to 6.2 require measurements at each microphone
location.
If the measurement is made with a radar device directed towards the vehicle from a road-side
location, the measured speed will be lower than the actual due to the angle error. It is important to
correct for the error due to this effect. If the instrument itself does not provide such a correction, the
reading shall be corrected manually.
See also the last paragraph of 9.6 for precautions regarding measurements for the “low” road speed
category.
8.5 Temperature measurement
8.5.1 General
Measurements of air temperature are mandatory, whereas measurement of road surface temperature
are recommended.
The measurements shall have a duration of at least 15 s. The thermometer manufacturer’s
instructions are to be observed. The result is the reading rounded to the nearest whole degree
Celsius.
If continuous monitoring is not available, temperature shall be measured at 15 min intervals.
Air temperature
8.5.2
The temperature sensor shall be positioned in an unobstructed location as close to the centre of the
test surface as is practical and safe, in such a way that it is exposed to the airflow and protected from
direct solar radiation. The latter may be achieved by a shading screen. The sensor should be
positioned I,0 m to I,5 m above the road surface level, to minimize the influence of road surface
thermal radiation at low airflows.
8.5.3 Road surface temperature
The temperature sensor shall be positioned at a location where the temperature is representative of
the temperature in the wheel tracks, and without interfering with the sound measurement.
If an instrument with a contact temperature sensor is used on rough road surfaces, heat-conductive
paste shall be applied between the surface and the sensor to ensure adequate thermal contact.
9 Normalization of data
91 . Regression analysis
A linear regression analysis of sound pressure levels on speed shall be made using data pairs
consisting of the maximum A-weighted sound level versus the logarithm (base 10) of speed for each
vehicle pass-by. A regression line shall be fit to the data points for each separate vehicle category,
using the least squares method.
NOTE -
Since speed is not the only factor determining vehicle sound emission, the correlation sound level-
speed may not always be high, particularly for heavy vehicles and for small speed ranges. This does not
preclude the calculated regression from being used for compensating as much as possible for speed influence.
IS0 118194 :1997(E)
9.2 Determination of Vehicle Sound Level at reference speeds
The reference speeds for the vehicle categories in the road speed categories are specified in table 1
below. Note that the reference speeds are the same for the two heavy vehicle groups.
The ordinate sound level of the regression line for each category of vehicle at the corresponding
reference speed is taken to be the Vehicle Sound Level, L,eh. In this way, for a certain road site, three
Lveh values are obtained: for cars, dual-axle heavy vehicles and multi-axle heavy vehicles.
All levels shall be calculated to two decimal places and rounded to one decimal place.
Table 1 - Reference speeds and weighting factors (IA&) in the different road speed categories
(the weighting factors refer to 9.5)
Road speed category
Vehicle category Low Medium High
Ref speed IA& Ref speed I& Ref speed IA&
No .
Name
[km/h]
[km/h] [km/h]
Cars 1 50 0,900 80 0,800 110 0,700
Dual-axle heavy
2a 50 0,075 70 0,100 85 0,075
vehicles
Multi-axle heavy
2b 50 0,025 70 0,100 85 0,225
vehicles
9.3 Useful speed range for the regression line
For the regression calculation and subsequent normalization to a reference speed the following
condition shall be met. The range of speeds covered by the measured vehicles shall be such that the
reference speed shall be within the range of plus-or-minus one standard deviation from the actually
measured average speed for heavy vehicles and plus-or-minus one-and-a-half standard deviation for
cars.
9.4 Correction of sound levels according to temperature
The Vehicle Sound Levels should be corrected to a reference air temperature of 20 “C. A suitable
method is at present under consideration. Both the uncorrected and the corrected levels shall be
reported. However, until a suitable correction method has been prepared, only uncorrected Lv&
values are mandatory to report.
Alternatively, if temperature measurements are made at each individual vehicle pass-by, along with
sound measurements, it is preferred to correct each measured sound level individually for
temperature instead of just the Vehicle Sound Level.
IS0 11819-l : 1997(E) @ IS0
9.5 Determination of the Statistical Pass-By Index (SPBI)
In order to obtain an aggregate (overall) level of road surface influence on traffic noise for a mix of
vehicles, a Statistical Pass-By Index shall be calculated as follows:
L& 0
L,llO
L2d1 ‘1 dB
SPBI = IO lg[W, x 10
+ W2a (dV2a) x 10
+ wb (hk2b) x lo
where
SPBI is the Statistical Pass-by Index, for a standard mix of light and heavy vehicles;
are the Vehicle Sound Levels for vehicle categories 1, 2a and 2b according to 9.2;
Lip L2a and L2b
are the weighting factors, which are equivalent to the assumed proportions of
wl y W2a and W2b
vehicle categories in the traffic, according to table 1;
are the reference speeds of individual vehicle categories, according to table 1.
6 9 V2a and V2b
Typical values for the weighting factors Wx (WI, W2a and w&) may vary considerably from place to
place, country to country and with time of day and night. The values selected in table 1 should
represent globally most typical cases which allow simple comparisons of road surfaces. However, it is
recognised that in many cases one would prefer to use other, perhaps nationally adapted factors as a
supplement. The mandatory reporting of all Lveh values allows such SPBI calculations to be made,
but when reporting these optional calculations the non-standard weighting factors used shall always
be duly specified.
In many cases the main use of the SPBI would be to compare a certain surface with a reference
surface according to Case 2 of clause 10, and present the result as a difference value. This difference
is the same as the difference measured in equivalent levels for the assumed reference speeds and
proportions of heavy vehicles according to table 1.
NOTE - SPBI is not an equivalent level (Leq) of traffic noise, but can be used to describe the relative influence
of the road surface on such levels. The SPBI is an index obtained by “energetically” adding the Lveh values
together, with each L veh weighted in accordance with the expected typical proportion of the vehicle category in
question. The index will numerically have a value close to the mean Lveh levels. It is valid for cases where
speeds of cars and heavy vehicles are as given in table 1. The index cannot be used for estimation of effects of
speed.
9.6 Measurement uncertainty
The expected random errors for single-site measurements (see 6.2), expressed as standard
deviations and confidence intervals, according to pre-normative research have been found to be as
presented in table 2. These are due mainly to variations in sound level between different vehicles
within the category in question. The standard deviation is the deviation with the speed effect removed,
i.e. based on the residuals around the regression line of sound level versus the (logarithm of) speed.
In the case of paired measurements (see 6.2) the errors are reduced. If instead the individual levels
for each vehicle on each site are studied (in pairs), the errors due to vehicle fleet variation will be
considerably reduced. This is because the studied vehicle fleet on each site will be identical.
In addition to the random errors, there are always systematic errors due to instrumentation and
calibration imperfections and due to deviations from ideal acoustical propagation conditions. The
systematic error due to measuring instruments is + 1 dB for the precision instrument system required
here. Another important uncertainty in this procedure is that of variations in vehicle fleet composition,
which may vary from place to place and time to time. The latter error may amount to 0,3 dB to 06 dB
within a “typical” European country (see reference [3] in annex F).
Repeatability according to IS0 572&l is better than 1,O dB according to reference [4] in annex F.
IS0 11819~1:1997( E)
@ IS0
Table 2 - Expected random errors in A-weighted sound pressure level
(rounded to one decimal).
/
Standard deviation for 95 % confidence interval
Vehicle class individual vehicles around Lveh
around
...